Analog front end for DTV, DTV system having the same, and operation methods thereof

ABSTRACT

Provided is an analog front end of a digital TV, a digital TV system having the same, and a method of operating the same. The analog front end includes: a first selection circuit which selectively outputs differential sound intermediate frequency signals or differential TV broadcast signals in response to a first selection signal; a second selection circuit which outputs a clock signal among a plurality of clock signals having a different sampling frequencies, in response to a second selection signal; and an analog-to-digital converter which converts output signals output from the first selection circuit to a digital code, according to a sampling frequency of a clock signal output from the second selection circuit.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional application of U.S. patent application Ser. No.13/450,035, filed Apr. 18, 2012, which claims priority under 35 U.S.C.§119(a) from Korean Patent Application Nos. 10-2011-0037515, filed onApr. 21, 2011 in the Korean Intellectual Property Office, and10-2011-0037516, filed on Apr. 21, 2011 in the Korean IntellectualProperty office, the disclosures of which are hereby incorporated byreference in their entireties.

BACKGROUND

Apparatuses and methods consistent with exemplary embodiments relate toan analog front end (AFE), and more particularly, to an analog front end(AFE) of a digital television (DTV) that may selectively process a soundintermediate frequency signal, differential DTV broadcast signals, anddifferential analog TV broadcast signals, a DTV system having the AFE,and operation methods thereof.

Digital televisions (DTVs) refer to a broadcasting system forbroadcasting and receiving video and audio by digital signals, incontrast to televisions using analog signals. The DTV uses data that iscompressed and modulated in a digital method so that the data may bewatched through television sets or set-top boxes designed for DTV.

The DTV has some merits over the analog televisions, including that abandwidth used by a channel may be reduced. Also, multicasting, that is,a function to broadcast various programs on a single channel at the sametime, and an electric program guide (EPG) are available in the DTV.

SUMMARY

Aspects of one or more exemplary embodiments provide an analog front endof a digital television (DTV) that may selectively process a soundintermediate frequency signal, differential DTV broadcast signals, anddifferential analog TV broadcast signals, according to an operationmode, a DTV system having the analog front end, and operation methodsthereof.

According to an aspect of an exemplary embodiment, there is provided ananalog front end (AFE) of a digital TV processing system, the AFEincluding: a first selection circuit which outputs differential soundintermediate frequency signals or differential TV broadcast signals inresponse to a first selection signal; a second selection circuit whichoutputs a clock signal among a plurality of clock signals havingdifferent sampling frequencies, in response to a second selectionsignal; and an analog-to-digital converter which converts the outputsignals output from the first selection circuit to a digital code,according to a sampling frequency of the output clock signal output fromthe second selection circuit.

According to an aspect of another exemplary embodiment, there isprovided a digital TV processing system including: a tuner whichgenerates at least one of a single-ended sound intermediate frequencysignal and differential TV broadcast signals from radio frequencysignals; an analog front end (AFE) which selectively processes thegenerated single-ended sound intermediate frequency signal and thegenerated differential TV broadcast signals; and a demodulator whichdemodulates a digital code output from the AFE, wherein the AFEincludes: a first selection circuit which outputs differential soundintermediate frequency signals generated based on the generatedsingle-ended sound intermediate frequency signal or the generateddifferential TV broadcast signals, in response to a first selectionsignal; a second selection circuit which outputs a clock signal among aplurality of clock signals having different sampling frequencies, inresponse to a second selection signal; and an analog-to-digitalconverter which converts the output signals output from the firstselection circuit to the digital code, according to a sampling frequencyof the output clock signal output from the second selection circuit.

According to an aspect of another exemplary embodiment, there isprovided a signal processing circuit including: an analog-to-digitalconverter which converts differential analog signals to a digital code,in response to a sampling clock signal; a fractional-N phase locked loop(PLL) which receives a clock signal as an input clock signal; and afirst selector which selectively outputs one of the clock signal and anoutput clock signal output from the fractional-N PLL as the samplingclock signal, in response to a first selection signal.

According to an aspect of another exemplary embodiment, there isprovided a digital TV processing system including: an analog front end(AFE) which converts differential TV broadcast signals to a digital codeaccording to a sampling clock signal; and a demodulator whichdemodulates the digital code, wherein the AFE includes: ananalog-to-digital converter which converts differential analog signalsto the digital code, in response to the sampling clock signal; afractional-N phase locked loop which receives a clock signal as an inputclock signal; and a first selector which selectively outputs one of theclock signal and an output clock signal output from the fractional-Nphase locked loop as the sampling clock signal, in response to a firstselection signal.

According to an aspect of another exemplary embodiment, there isprovided a signal processing method of a digital TV processing system,the signal processing method including: selectively outputtingdifferential sound intermediate frequency signals or differential TVbroadcast signals in response to a first selection signal; outputting aclock signal among a plurality of clock signals having differentsampling frequencies, in response to a second selection signal; andconverting the output signals output from the selectively outputting toa digital code, according to a sampling frequency of the output clocksignal.

According to an aspect of another exemplary embodiment, there isprovided a signal processing method including: converting differentialanalog signals to a digital code, in response to a sampling clocksignal; receiving, by a fractional-N phase locked loop (PLL), a clocksignal as an input clock signal; and selectively outputting, by a firstselector, one of the clock signal and an output clock signal output fromthe fractional-N PLL as the sampling clock signal, in response to afirst selection signal.

According to an aspect of another exemplary embodiment, there isprovided a method of manufacturing an analog front end (AFE) of adigital TV processing system, the method including: providing, in afirst region of a semiconductor substrate, a first selection circuit foroutputting differential sound intermediate frequency signals ordifferential TV broadcast signals in response to a first selectionsignal; providing, in a second region of the semiconductor substrate, asecond selection circuit for outputting a clock signal among a pluralityof clock signals having different sampling frequencies, in response to asecond selection signal; and providing, in a third region of thesemiconductor substrate, an analog-to-digital converter for convertingthe output signals output from the first selection circuit to a digitalcode, according to a sampling frequency of the output clock signaloutput from the second selection circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments will be more clearly understood from the followingdetailed description taken in conjunction with the accompanying drawingsin which:

FIG. 1 is a block diagram schematically showing a digital television(DTV) system according to an exemplary embodiment;

FIG. 2 is a block diagram of an analog front end of FIG. 1, according toan exemplary embodiment;

FIG. 3 is a block diagram of an analog front end of FIG. 1, according toanother exemplary embodiment;

FIG. 4 is a block diagram schematically showing a DTV system accordingto another exemplary embodiment;

FIG. 5 is a block diagram of an analog front end of FIG. 4, according toan exemplary embodiment;

FIG. 6 is a waveform diagram of a plurality of system clock signals ofFIG. 5;

FIG. 7 is a flowchart for explaining a method of operating the analogfront end of FIG. 1;

FIG. 8 is a flowchart for explaining a method of operating the DTVsystem of FIG. 1;

FIG. 9 is a flowchart for explaining a method of manufacturing theanalog front end of FIG. 1; and

FIG. 10 is a flowchart for explaining an operation of the DTV system ofFIG. 4.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The attached drawings for illustrating exemplary embodiments arereferred to in order to gain a sufficient understanding of exemplaryembodiments and the merits thereof. Hereinafter, exemplary embodimentswill be described in detail with reference to the attached drawings, inwhich like reference numerals in the drawings denote like elements.

FIG. 1 is a block diagram schematically showing a digital television(DTV) system 10 according to an exemplary embodiment. Referring to FIG.1, the DTV system 10 may be embodied by a satellite DTV system, a cableDTV system, a handheld DTV system, a terrestrial DTV system, etc. TheDTV system 10 includes a high definition (HD) TV system, an imageprocessing device, etc. The handheld DTV system may be embodied bymobile phones, smart phones, tablet personal computers (PCs), carnavigation systems, personal digital assistants (PDAs), portablemultimedia players (PMPs), etc.

The DTV system 10 may include a tuner 20, an analog front end (AFE) 30,a demodulator 40, and a decoder 50. According to various exemplaryembodiments, the AFE 30, the demodulator 40, and the decoder 50 may beintegrated in a single integrated circuit (IC), and the turner 20 mayalso be integrated in the single IC.

The tuner 20 includes appropriate circuits, logics, and/or codes, andmay obtain radio frequency (RF) signals RF and generate a single-endedsound intermediate frequency signal SIF_IN and/or differential TVbroadcast signals CHIF_INP and CHIF_INN from the RF.

The differential TV broadcast signals CHIF_INP and CHIF_INN may includedifferential digital TV broadcast signals, for example, DTV videosignals and DTV sound intermediate frequency signals. Also, thedifferential TV broadcast signals CHIF_INP and CHIF_INN may includedifferential analog TV broadcast signals, for example, analog videosignals and analog sound intermediate frequency signals.

According to an exemplary embodiment, the differential digital TVbroadcast signals, that is, the DTV video signals and the DTV soundintermediate frequency signals, may be signals according to a digitalvideo broadcasting (DVB) family that is a DTV standard in Europe, forexample, DVB-S (satellite), DVB-T (terrestrial), DVB-C (cable), DVB-H(handheld), or DVB-SH (satellite services to handheld).

According to another exemplary embodiment, the differential digital TVbroadcast signals, that is, the DTV video signals and the DTV soundintermediate frequency signals, may be signals corresponding to anadvanced television system committee (ATSC) family that is a DTVstandard in North America, for example, ATSC (terrestrial/cable) orATSC-M/H (mobile/handheld).

According to still another exemplary embodiment, the differentialdigital TV broadcast signals, that is, the DTV video signals and the DTVsound intermediate frequency signals, may be signals appropriate for anintegrated services digital broadcasting (ISDB) that is a DTV standardin Japan and Latin America, for example, ISDB-S (satellite), ISDB-T(terrestrial), ISDB-C (cable), and 1seg (handheld). The 1seg is mobileterrestrial digital sound intermediate frequency/video and databroadcasting services used in Japan, Chile, Peru, and Argentina.

According to still another exemplary embodiment, the differentialdigital TV broadcast signals, that is, the DTV video signals and the DTVsound intermediate frequency signals, may be signals satisfying ISDB-Tb(international system for digital broadcast, terrestrial, Brazilianversion) that is a DTV standard in Brazil, Argentina, Chile, Peru,Venezuela, Bolivia, Ecuador, Costa Rica, and Uruguay.

According to still another exemplary embodiment, the differentialdigital TV broadcast signals, that is, the DTV video signals and the DTVsound intermediate frequency signals, may be signals satisfying Chinadigital multimedia broadcasting-terrestrial/handheld (CDMB-T/H) or Chinamobile multimedia broadcasting (CMMB) that is a DTV standard in China.

According to still another exemplary embodiment, the differentialdigital TV broadcast signals, that is, the DTV video signals and the DTVsound intermediate frequency signals, may be signals satisfyingterrestrial-digital multimedia broadcasting (T-DMB) or satellite-digitalmultimedia broadcasting (S-DMB) that is a DTV standard in Korea.

According to another exemplary embodiment, the differential analog TVbroadcast signals, that is, the analog video signals and the analogsound intermediate frequency signals, may be signals appropriate fornational television system committee (NTSC), phase alternating line(PAL), or sequential color with memory (SECAM).

The AFE 30 that may be integrated in a single chip may process, forexample, analog-to-digital convert, the single-ended sound intermediatefrequency signal SIF_IN or the differential TV broadcast signalsCHIF_INP and CHIF_INN, and output a digital code AFE_OUT according to aprocessing result. The demodulator 40 may demodulate the digital codeAFE_OUT output from the AFE 30, and the decoder 50 may decode thedemodulated digital code demodulated by the demodulator 40.

FIG. 2 is a block diagram of the AFE 30 of FIG. 1, according to anexemplary embodiment. Referring to FIGS. 1 and 2, the analog front end(AFE) 30 a of FIG. 2 that is an exemplary embodiment of the AFE 30 ofFIG. 1 includes a first selection circuit (or a first processingcircuit) 32, a second selection circuit (or a second processing circuit)34 a, and an analog-to-digital converter (ADC) 36.

The first selection circuit 32, in response to a first selection signalSIG_SEL, selectively outputs the differential TV broadcast signalsCHIF_INP and CHIF_INN or differential sound intermediate frequencysignals AP and AN, or IDAP and IDAN, which are generated based on thesingle-ended sound intermediate frequency signal SIF_IN. The secondselection circuit 34 a, in response to a second selection signal SEL2,selectively outputs any one of a plurality of clock signals havingdifferent sampling frequencies f1, f2, f3, or f4, to the ADC 36.

The ADC 36 may convert the differential output signals of the firstselection circuit 32 to a digital code AFE_OUT according to the samplingfrequencies f1, f2, f3, or f4 of the clock signal selectively output bythe second selection circuit 34 a. The digital code AFE_OUT may be Mbits where M is a natural number, for example, 10 or 12 (i.e., M=10 orM=12).

The first selection circuit 32 includes a single-to-differentialconverter 32-1, a first multiplexer 32-2, and a second multiplexer 32-3.The single-to-differential converter 32-1 converts the single-endedsound intermediate frequency signal SIF_IN to the differential soundintermediate frequency signals AP and AN, or IDAP or IDAN.

The single-to-differential converter 32-1 includes a direct current (DC)signal generator 32-11 and a programmable gain amplifier (PGA) 32-12.

The DC signal generator 32-11 sets a DC level on the single-ended soundintermediate frequency signal SIF_IN and outputs the first differentialsound intermediate frequency signals IDAP and IDAN on which a DC levelis set. The PGA 32-12 controls, for example, increases or decreases,gain of each of the first differential sound intermediate frequencysignals IDAP and IDAN to output the differential sound intermediatefrequency signals AP and AN. Any one (e.g., IDAP) of the firstdifferential sound intermediate frequency signals IDAP and IDANgenerated by the DC signal generator 32-11 is supplied to the firstmultiplexer 32-2, whereas the other one (e.g., IDAN) of the firstdifferential sound intermediate frequency signals IDAP and IDAN issupplied to the second multiplexer 32-3.

Although FIG. 2 illustrates that the first differential soundintermediate frequency signals IDAP and IDAN are respectively suppliedto input terminals of the first and second multiplexers 32-2 and 32-3,the first differential sound intermediate frequency signals IDAP andIDAN may not be respectively supplied to input terminals of the firstand second multiplexers 32-2 and 32-3 in some exemplary embodiments.

The first multiplexer 32-2, in response to the first selection signalSIG_SEL, selectively outputs any one, for example, AP or IDAP, of thedifferential sound intermediate frequency signals AP and AN, or IDAP andIDAN, or any one, for example, CHIF_INP, of the differential TVbroadcast signals CHIF_INP and CHIF_INN, to the ADC 36. The secondmultiplexer 32-3, in response to the first selection signal SIG_SEL,selectively outputs the other one, for example, AN or IDAN, of thedifferential sound intermediate frequency signals AP and AN, or IDAP andIDAN, or the other one, for example, CHIF_INN, of the differential TVbroadcast signals CHIF_INP and CHIF_INN, to the ADC 36. The firstselection signal SIG_SEL may include one or more bits.

For example, when the first selection circuit 32 is operated in a firstoperation mode in which the differential sound intermediate frequencysignals AP and AN, or IDAP and IDAN, are output or processed, the firstand second multiplexers 32-2 and 32-3, in response to the firstselection signal SIG_SEL, output the differential sound intermediatefrequency signals AP and AN, or IDAP and IDAN, having carrierfrequencies of several megahertz (MHz), to the ADC 36. However, when thefirst selection circuit 32 is operated in a second operation mode inwhich the differential TV broadcast signals CHIF_INP and CHIF_INN areoutput or processed, the first and second multiplexers 32-2 and 32-3, inresponse to the first selection signal SIG_SEL, output the differentialTV broadcast signals CHIF_INP and CHIF_INN, having carrier frequenciesof tens of megahertz (MHz), to the ADC 36.

The second selection circuit 34 a may include a first frequency divider34-1, a third multiplexer 34-2, a phase locked loop (PLL) 34-3, and afourth multiplexer 34-5. The first frequency divider 34-1 may divide thefirst frequency f1 of a source clock signal CLK_IN that is externallyinput by a division ratio K, where K is a real number, and generate adivided clock signal having the second frequency f2.

The third multiplexer 34-2, in response to a clock selection signalSELC, may selectively output the source clock signal CLK_IN and thedivided clock signal output from the first frequency divider 34-1. ThePLL 34-3 receives the clock signal output from the third multiplexer34-2 as an input clock signal and outputs a low jitter PLL clock signalhaving the third frequency f3. The fourth multiplexer 34-5, in responseto the second selection signal SEL2, selectively outputs the clocksignal output from the third multiplexer 34-2 and the PLL clock signaloutput from the PLL 34-3. The clock selection signal SELC or the secondselection signal SEL2 may include one or more bits.

In some exemplary embodiments, the second selection circuit 34 a mayfurther include a second frequency divider 34-4 embodied outside the PLL34-3. The second frequency divider 34-4 may divide the third frequencyf3 of the PLL clock signal output from the PLL 34-3 by a division ratioL, where L is a real number, and generate a divided clock signal havingthe fourth frequency f4. Thus, the fourth multiplexer 34-5 selectivelyoutputs any one of a plurality of clock signals having differentsampling frequencies f1, f2, f3, and f4, to the ADC 36, according to thesecond selection signal SEL2.

For example, in the first or second operation mode, the carrierfrequency of the sampling frequencies f1, f2, f3, or f4 of the clocksignal output from the second selection circuit 34 may be tens ofmegahertz (MHz). However, the carrier frequency of each samplingfrequency f1, f2, f3, or f4 may vary according to design specifications.

As shown in FIGS. 1 and 2, a single AFE (30 or 30 a) has an effect ofselectively processing the single-ended sound intermediate frequencysignal SIF_IN or the differential TV broadcast signals CHIF_INP andCHIF_INN according to an operation mode, for example, the firstoperation mode or the second operation mode.

Also, since the AFE 30 a may generate the respective samplingfrequencies f1, f2, f3, and f4 for sampling the single-ended soundintermediate frequency signal SIF_IN, the differential digital TVbroadcast signals, or the differential analog TV broadcast signalsaccording to various DTV standards, using the PLL 34-3 embodied inside,the AFE 30 a has an effect of being commonly used for DTVs using theabove-described various DTV standards. In some exemplary embodiments, asampling clock signal output from the second selection circuit 34 a maybe provided as an operation clock signal of the demodulator 40 of FIG.1.

FIG. 3 is a block diagram of the AFE 30 of FIG. 1, according to anotherexemplary embodiment. Referring to FIGS. 2 and 3, except for a secondselection circuit or second processing circuit 34 b of FIG. 3, thestructure of the AFE 30 b of FIG. 3 is substantially the same as orsimilar to that of the AFE 30 a of FIG. 2.

The second selection circuit 34 b includes a fractional-N phase lockedloop (PLL) 111 and a selection circuit 113. For example, the selectioncircuit 113 may be embodied by a multiplexer. The fractional-N PLL 111that is used as an example of a frequency synthesizer may receive thesource clock signal CLK_IN as an input clock signal and generate a clocksignal. The fractional-N PLL 111 may not only reduce a lock-up time butalso reduce phase noise.

The selection circuit 113, in response to a selection signal SEL11,outputs any one of the source clock signal CLK_IN and the clock signaloutput from the fractional-N PLL 111 as a sampling clock signal, to theADC 36. For example, when the selection signal SEL11 is at a firstlevel, for example, a low level, the selection circuit 113 may outputthe source clock signal CLK_IN. When the selection signal SEL11 is at asecond level, for example, a high level, the selection circuit 113 mayoutput the output clock signal of the fractional-N PLL 111.

The ADC 36 may convert the output signals CHIF_INP and CHIF_INN, AP andAN, or IDAP and IDAN of the first selection circuit 32 to a digital codeAFE_OUT according to a sampling frequency of the clock signalselectively output by the second selection circuit 34 b. In someexemplary embodiments, the sampling clock signal output from the secondselection circuit 34 b may be provided as an operation clock signal ofthe demodulator 40 of FIG. 1.

FIG. 4 is a block diagram schematically showing a DTV system 10 aaccording to another exemplary embodiment. Referring to FIG. 4, the DTVsystem 10 a is another example of the DTV system 10 of FIG. 1 and mayinclude the tuner 20, an AFE 30-1, a demodulator 40-1, and the decoder50.

The AFE 30-1 may further generate a plurality of system clock signalsSysCLK0, SysCLK1, and SysCLK2 in addition to a sampling clock signalADCCLK. No skew exists between the sampling clock signal ADCCLK and eachof the plurality of system clock signals SysCLK0, SysCLK1, and SysCLK2,as shown in FIG. 6. For example, a rising edge (or a falling edge) ofthe sampling clock signal ADCCLK and a rising edge (or a falling edge)of each of the plurality of system clock signals SysCLK0, SysCLK1, andSysCLK2 are aligned in terms of time. The sampling clock signal ADCCLKand each of the plurality of system clock signals SysCLK0, SysCLK1, andSysCLK2 may be described as synchronized with each other. Thedemodulator 40-1 may demodulate the digital code AFE_OUT using at leastone of the sampling clock signal ADCCLK and the plurality of systemclock signals SysCLK0, SysCLK1, and SysCLK2.

FIG. 5 is a block diagram of the AFE 30-1 of FIG. 4, according to anexemplary embodiment. Referring to FIGS. 2 and 5, except for a secondselection circuit or second processing circuit 34 c of FIG. 5, thestructure of the AFE 30 c of FIG. 5 is substantially the same as orsimilar to that of the AFE 30 a of FIG. 2.

The second selection circuit 34 c includes a fractional-N PLL 134, afirst selector 136, a deskew frequency divider 137, and a secondselector 139. For example, each of the selectors 136 and 139 may beembodied by a multiplexer.

The fractional-N PLL 134 may receive the source clock signal CLK_IN asan input clock signal and generate a clock signal.

The first selector 136, in response to a selection signal SEL21,selectively outputs any one of the source clock signal CLK_IN and theoutput clock signal of the fractional-N PLL 134. The deskew frequencydivider 137 divides a frequency of a clock signal DCLK output from thefirst selector 136 and generates the plurality of system clock signalsSysCLK0, SysCLK1, and SysCLK2 having no skew between each other. Thefrequencies of the plurality of system clock signals SysCLK0, SysCLK1,and SysCLK2 are different from each other.

The deskew frequency divider 137 includes a first frequency divider137-1 and a second frequency divider 137-2. The first frequency divider137-1 divides a frequency of the DCLK of the first selector 136 by afirst division ratio N1 and generates a first system clock signalSysCLK0 having a divided frequency. The second frequency divider 137-2divides a frequency of the output clock signal of the first frequencydivider 137-1 by a second division ratio N2.

The first division ratio N1 that is a natural number may be adjustedaccording to a first code CODE1 that is externally input, and the seconddivision ratio N2 that is a natural number may be adjusted according toa second code CODE2 that is externally input.

The deskew frequency divider 137 may further include a third frequencydivider 137-3 and a fourth frequency divider 137-4. The third frequencydivider 137-3 divides a frequency of the clock signal DCLK of the firstselector 136 by a third division ratio N3 and generates a second systemclock signal SysCLK1 having a divided frequency. The fourth frequencydivider 137-4 divides a frequency of the clock signal DCLK of the firstselector 136 by a fourth division ratio N4 and generates a third systemclock signal SysCLK3 having a divided frequency.

The third division ratio N3 that is a natural number may be adjustedaccording to a third code CODE3 that is externally input, and the fourthdivision ratio N4 that is a natural number may be adjusted according toa fourth code CODE4 that is externally input. Each of the divisionratios N1-N4 may be reset or initialized by a reset signal RST.

Although FIG. 5 illustrates the deskew frequency divider 137 thatgenerates three system clock signals SysCLK0, SysCLK1, and SysCLK2 forconvenience of explanation, in some exemplary embodiments, the deskewfrequency divider 137 may include a plurality of frequency dividers,each being capable of dividing a frequency of the clock signal DCLK ofthe first selector 136 by different division ratios.

The second selector 139, in response to a second selection signal SEL22,outputs the clock signal DCLK output from the first selector 136 or theclock signal output from the second frequency divider 137-2 as thesampling clock signal ADCCLK. Thus, the ADC 36, in response to thesampling clock signal ADCCLK output from the second selector 139, mayconvert the output signals CHIF_INP and CHIF_INN, AP and AN, or IDAP andIDAN output from the first selection circuit 32, to the digital codeAFE_OUT.

Referring to FIGS. 4 and 5, the plurality of clock signals ADCCLK,SysCLK0, SysCLK1, and SysCLK2 may be supplied to the demodulator 40-1.The demodulator 40-1 may demodulate the digital code AFE_OUT using atleast one of the plurality of clock signals ADCCLK, SysCLK0, SysCLK1,and SysCLK2 output from the AFE 30-1.

In some exemplary embodiments, at least one of the plurality of clocksignals ADCCLK, SysCLK0, SysCLK1, and SysCLK2 output from the AFE 30-1,that is, the second selection circuit 34 c, may be used as an operationclock signal of the decoder 50 or an operation clock signal of aninternal circuit (not shown) embodied in the DTV system 10.

FIG. 6 is a waveform diagram of the system clock signals of FIG. 5. FIG.6 shows waveforms of the system clock signals when the first divisionratio N1 is 2, the second division ratio N2 is 3, and the fourthdivision ratio N4 is 1024.

In some exemplary embodiments, each of the frequency dividers 137-1 to137-4 may include a plurality of sub-frequency dividers (not shown)having different frequency division ratios. An output signal of each ofthe sub-frequency dividers may be selectively output according to eachcode CODE1 to CODE4.

FIG. 7 is a flowchart for explaining a method of operating the analogfront end 30 of FIG. 1. Referring to FIGS. 1 to 7, the first selectioncircuit 32 outputs the differential sound intermediate frequency signalsAP and AN or the IDAP and IDAN, or the differential TV broadcast signalsCHIF_INP and CHIF_INN according to the first selection signal SIG_SEL(operation S10).

The second selection circuit 34 a, 34 b, or 34 c may selectively outputany one of a plurality of clock signals having different samplingfrequencies according to the selection signal SEL2, SEL11, or SEL22(operation S20). The ADC 36 may convert the differential soundintermediate frequency signals AP and AN or the IDAP and IDAN, or thedifferential TV broadcast signals CHIF_INP and CHIF_INN output from thefirst selection circuit 32, to the digital code AFE_OUT, according to asampling frequency of a clock signal that is selectively output by thesecond selection circuit 34 a, 34 b, or 34 c (operation S30).

FIG. 8 is a flowchart for explaining a method of operating the DTVsystem 10 of FIG. 1. Referring to FIGS. 1 to 8, an operation method ofthe DTV system 10 including the tuner 20 that generates the single-endedsound intermediate frequency signal SIF_IN and/or the differential TVbroadcast signals CHIF_INP and CHIF_INN from radio frequency (RF)signals and the AFE 30 that generates the digital code AFE_OUT from thesingle-ended sound intermediate frequency signal SIF_IN or thedifferential TV broadcast signals CHIF_INP and CHIF_INN.

The tuner 20 generates the single-ended sound intermediate frequencysignal SIF_IN and/or the differential TV broadcast signals CHIF_INP andCHIF_INN from the RF signals (operation S2). The single-to-differentialconverter 32-1 of the AFE 30 generates the differential soundintermediate frequency signals AP and AN, or the IDAP and IDAN from thesingle-ended sound intermediate frequency signal SIF_IN (operation S4).

The first selection circuit 32 selectively outputs the differentialsound intermediate frequency signals AP and AN or the IDAP and IDAN, orthe differential TV broadcast signals CHIF_INP and CHIF_INN to the ADC36 according to the first selection signal SIG_SEL (operation S10). Thesecond selection circuit 34 a, 34 b, or 34 c may selectively output anyone of a plurality of clock signals having different samplingfrequencies according to the selection signal SEL2, SEL11, or SEL22(operation S20).

The ADC 36 may convert the differential sound intermediate frequencysignals AP and AN or the IDAP and IDAN, or the differential TV broadcastsignals CHIF_INP and CHIF_INN output from the first selection circuit 32to the digital code AFE_CODE according to a sampling frequency of theclock signal selectively output by the second selection circuit 34 a, 34b, or 34 c (operation S30).

The demodulator 40 demodulates the digital code AFE_OUT (operation S40)and the decoder 50 decodes the demodulated digital code (operation S50).

FIG. 9 is a flowchart for explaining a method of manufacturing theanalog front end of FIG. 1. Referring to FIGS. 1, 2, 3, 5, and 9, themethod of manufacturing the AFE 30 of a DTV is described as follows.

The first selection circuit 32 for outputting the differential soundintermediate frequency signals AP and AN or the IDAP and IDAN, or thedifferential TV broadcast signals CHIF_INP and CHIF_INN, for example,according to a signal SIG_SEL determining an operation mode, is formedor provided in a first region of a semiconductor substrate (operationS110).

The second selection circuit 34 a, 34 b, or 34 c for selectivelyoutputting any one of a plurality of clock signals having differentsampling frequencies according to the selection signal SEL2, SEL22, orSEL22 is formed or provided in a second region of the semiconductorsubstrate (operation S120).

The ADC 36 for converting the output signals of the first selectioncircuit 32 to the digital code AFE_OUT according to a sampling frequencyof the clock signal output from the second selection circuit 34 a, 34 b,or 34 c is formed or provided in a third region of the semiconductorsubstrate (operation S130).

The operations S110, S120, and S130 are separated for convenience ofexplanation, and each of the operations S110, S120, and S130 may beperformed simultaneously or at different times according to amanufacturing process of the AFE 30. At least a part of the firstregion, at least a part of the second region, and/or at least a part ofthe third region may be horizontally or vertically overlapped with oneanother.

FIG. 10 is a flowchart for explaining an operation of the DTV system 10a of FIG. 4. The operation of the DTV system 10 a is described asfollows with reference to FIGS. 4, 5, 6, and 10.

The fractional-N PLL 134 generates a PLL clock signal using the sourceclock signal CLK_IN (operation S210). The first selector 136, inresponse to the selection signal SEL21, selectively outputs any one ofthe source clock signal CLK_IN and the PLL clock signal (operationS220). As shown in FIG. 3 or 5, the clock signal output from theselection circuit 113 or 136 my be used as a sampling clock signal ofthe ADC 36.

The deskew frequency divider 137 generates a plurality of system clocksignals having no skew therebetween, for example, the deskew systemclock signals SysCLK0, SysCLK1, and SysCLK2, using the clock signal DCLKoutput from the first selector 136, a shown in FIG. 6 (operation S230).A rising edge (or a falling edge) of each of the system clock signalsSysCLK0, SysCLK1, and SysCLK2 and a rising edge (or a falling edge) ofthe clock signal DCLK output from the first selector 136 are aligned interms of time. Thus, no skew exists between each of the system clocksignals SysCLK0, SysCLK1, and SysCLK2 and the clock signal DCLK outputfrom the first selector 136.

The second selector 139, in response to the selection signal SEL22,outputs the clock signal DCLK output from the first selector 136 or theclock signal of the first frequency divider 137-2 as the sampling clocksignal ADCCLK (operation S240). The ADC 36 converts the differentialanalog signals to an M-bit digital code AFE_OUT using the sampling clocksignal ADCCLK (operation S250). The demodulator 40-1 demodulates theM-bit digital code AFE_OUT using at least one of the clock signalsADCCLK, SysCLK0, SysCLK1, and SysCLK2 output from the AFE 30-1(operation S260).

As described above with reference to FIG. 3, the signal processingcircuit including the fractional-N PLL 111, the selection circuit 113,and the ADC 36 may be applied to all signal processing circuits that arecapable of converting analog differential signals to a digital codeusing the sampling clock signal ADCCLK. The demodulator included in thesignal processing circuit may demodulate the digital code output fromthe ADC 36 using the sampling clock signal ADCCLK.

Also, as described above with reference to FIG. 5, the signal processingcircuit including the fractional-N PLL 134, the deskew frequency divider137, the selection circuits 136 and 139, and the ADC 36 may be appliedto all signal processing circuits that are capable of converting analogdifferential signals to a digital code using the sampling clock signalADCCLK.

The demodulator included in the signal processing circuit may demodulatethe digital code output from the ADC 36 using at least one of the clocksignals ADCCLK, SysCLK0, SysCLK1, and SysCLK2 output from the deskewfrequency divider 137. The analog front end according to exemplaryembodiments has an effect of selectively processing the soundintermediate frequency signal, the differential DTV broadcast signals,and the differential analog TV broadcast signals according to anoperation mode. Also, the analog front end including a phase locked loophas an effect of generating a sampling frequency including low jitterthat may be commonly used for various DTV standards.

The analog front end according to exemplary embodiments has an effect ofsimultaneously generating various system clock signals used in a DTVsystem and a sampling clock signal that may convert the differentialanalog signals to a digital code.

While exemplary embodiments have been particularly shown and describedabove, it will be understood that various changes in form and detailsmay be made therein without departing from the spirit and scope ofpresent inventive concept.

What is claimed is:
 1. A signal processing circuit comprising: ananalog-to-digital converter which converts differential analog signalsto a digital code, in response to a sampling clock signal input to theanalog-to-digital converter; a fractional-N phase locked loop (PLL)which receives a clock signal as an input clock signal; and a firstselector which receives the clock signal and an output clock signaloutput from the fractional-N PLL, and which selectively outputs, inresponse to a first selection signal, one of the received clock signaland the received output clock signal as the sampling clock signal. 2.The signal processing circuit of claim 1, further comprising: a firstfrequency divider which divides a frequency of an output clock signaloutput from the first selector by a first division ratio; a secondfrequency divider which divides a frequency of an output clock signaloutput from the first frequency divider by a second division ratio; anda second selector which selectively outputs one of the output clocksignal output from the first selector and an output clock signal outputfrom the second frequency divider as the sampling clock signal, inresponse to a second selection signal.
 3. The signal processing circuitof claim 2, wherein the signal processing circuit is an analog front endof a digital TV processing device.
 4. The signal processing circuit ofclaim 2, further comprising a demodulator which demodulates the digitalcode using at least one of the sampling clock signal output from thesecond selector and the output clock signal output from the firstfrequency divider.
 5. The signal processing circuit of claim 2, whereinthe sampling clock signal output from the second selector and the outputclock signal output from the first frequency divider are synchronizedwith each other.
 6. A digital TV processing system comprising: an analogfront end (AFE) which converts differential TV broadcast signals to adigital code according to a sampling clock signal; and a demodulatorwhich demodulates the digital code, wherein the AFE comprises: ananalog-to-digital converter which converts differential analog signalsto the digital code, in response to the sampling clock signal input tothe analog-to-digital converter; a fractional-N phase locked loop whichreceives a clock signal as an input clock signal; and a first selectorwhich receives the clock signal and an output clock signal output fromthe fractional-N PLL, and which selectively outputs, in response to afirst selection signal, one of the received clock signal and thereceived output clock signal as the sampling clock signal.
 7. Thedigital TV processing system of claim 6, wherein the AFE furthercomprises: a first frequency divider which divides a frequency of anoutput clock signal output from the first selector by a first divisionratio; a second frequency divider which divides a frequency of an outputclock signal output from the first frequency divider by a seconddivision ratio; and a second selector which selectively outputs one ofthe output clock signal output from the first selector and an outputclock signal output from the second frequency divider as the samplingclock signal, in response to a second selection signal, wherein thedemodulator demodulates the digital code using at least one of thesampling clock signal and the output clock signal output from the firstfrequency divider.
 8. The digital TV processing system of claim 6,wherein the AFE further comprises: a first frequency divider whichdivides a frequency of an output clock signal output from the firstselector by a first division ratio; a second frequency divider whichdivides a frequency of an output clock signal output from the firstfrequency divider by a second division ratio; a third frequency dividerwhich divides a frequency of an output clock signal output from thefirst selector by a third division ratio; and a second selectorselectively outputs one of a clock signal output from the first selectoror an output clock signal output from the second frequency divider asthe sampling clock signal, in response to a second selection signal,wherein the demodulator demodulates the digital code using at least oneof the sampling clock signal, the output clock signal output from thefirst frequency divider, and an output clock signal output from thethird frequency divider.
 9. A signal processing method comprising:converting, by an analog-to-digital converter, differential analogsignals to a digital code, in response to a sampling clock signal inputto the analog-to-digital converter; receiving, by a fractional-N phaselocked loop (PLL), a clock signal as an input clock signal; andreceiving, by a first selector, the clock signal and an output clocksignal output from the fractional-N PLL, and selectively outputting, bythe first selector in response to a first selection signal, one of thereceived clock signal and the received output clock signal as thesampling clock signal.
 10. The signal processing method of claim 9,further comprising: dividing, by a first frequency divider, a frequencyof an output clock signal output from the first selector by a firstdivision ratio; dividing, by a second frequency divider, a frequency ofan output clock signal output from the first frequency divider by asecond division ratio; and selectively outputting, by a second selector,one of the output clock signal output from the first selector and anoutput clock signal output from the second frequency divider as thesampling clock signal, in response to a second selection signal.
 11. Thesignal processing method of claim 10, further comprising demodulatingthe digital code using at least one of the sampling clock signal outputfrom the second selector and the output clock signal output from thefirst frequency divider.
 12. The signal processing method of claim 10,wherein the sampling clock signal output from the second selector andthe output clock signal output from the first frequency divider aresynchronized with each other.
 13. The signal processing circuit of claim1, further comprising: a first selection circuit which outputsdifferential analog sound intermediate frequency signals or differentialanalog TV broadcast signals in response to a second selection signal,wherein the analog-to-digital converter converts the output signalsoutput from the first selection circuit to the digital code, accordingto a sampling frequency of the sampling clock signal.
 14. The digital TVprocessing system of claim 6, wherein the AFE further comprises: a firstselection circuit which outputs differential sound intermediatefrequency signals or the differential TV broadcast signals in responseto a second selection signal, wherein the analog-to-digital converterconverts the output signals output from the first selection circuit tothe digital code, according to a sampling frequency of the samplingclock signal.
 15. The signal processing method of claim 9, furthercomprising: outputting, by a first selection circuit, differentialanalog sound intermediate frequency signals or differential analog TVbroadcast signals in response to a second selection signal, wherein theconverting comprises converting the output signals output from the firstselection circuit to the digital code, according to a sampling frequencyof the sampling clock signal.